If I send a 50hz signal to a woofer for 1 second, it should go forth and back 50 times. Anything more or less would produce a different tone than 50 hz. It can only do 50 hz if it moves in a particular speed. If it moves faster, it does more than 50hz, if it does slower it cannot do 50hz.
So if you measure the drivers distortion, and if it shows none of these behavior, we can now assume the driver is distortion free.
Is that enough for for accurate 50hz at your listening spot? No.
assume two signals with 50 hz of 1 second duration separated by a 0.5 second between them
In a typical Room with reflections, assume you get a wave with 50 to and fro vibrations reaching your spot as the direct wave from the first and second signal.
The room has reflections, and reflected wave takes longer time to reach you and if it’s still loud enough you would never perceive the gap between the waves due to this effect here .
en.m.wikipedia.org